A North Carolina police officer pulled over Nicholas Heien because one of his car’s brake lights was out. The state’s law requires only one light to be working, so the stop was based on a mistake of law.

After Heien was pulled over, he gave consent for the officer to search his car. The officer found cocaine in the car, then placed Heien under arrest.

Why is this such a big deal? Because the decision "lowered the bar of expectations for all sorts of government searches and seizures":

Chief Justice John Roberts’ creative and harmful majority opinion in Heien claims precedent, writing that the “ultimate touchstone of the Fourth Amendment is ‘reasonableness.’ ”

Repeating such lines often enough in case law sometimes gives fluff the appearance of substantive and controlling law. But it is inherently unreasonable that mistakes of law may make lawful what should be unlawful.

Roberts also relies on early American case law about personal liability of federal inspectors and tax collectors. There was a time when federal search and seizure officials could be sued for trespass. That is a practice that should be brought back, but Roberts, joined by the court’s originalists, misapplies those cases to create a new Fourth Amendment interpretation that weakens the rule of law over government.

Lone dissenter Justice Sonia Sotomayor grasps what is at stake when she writes, “The meaning of the law is not probabilistic in the same way that factual determinations are. Rather, ‘the notion that the law is definite and knowable’ sits at the foundation of our legal system. ... Departing from this tradition means further eroding the Fourth Amendment’s protection of civil liberties in a context where that protection has already been worn down.”

This is hardly the first time governments have played fast and loose with the clear meaning of the law.

But now, it appears as though the Court, too, is willing to play Scrabble with the Bill of Rights. That is dangerous.